marginal utilities, or, as it is sometimes expressed, their marginal
net products.

Whenever, therefore, the proportions in which two or more things are
produced or used together can be varied, the relations of joint supply
and joint demand are perfectly consistent with a specific marginal
cost and marginal utility for each commodity.


§3. _A contrast between Cotton and Cotton-seed, and Wool and
Mutton_. But it sometimes happens that such variations cannot be
made. Thus, it has not been found possible (so far as I am aware) to
alter the proportions in which cotton lint and cotton-seed are yielded
by the cotton plant. Roughly speaking, you get about 2 pounds of
cotton-seed for every 1 pound of cotton lint (or raw cotton), and
though this proportion may vary somewhat from plantation to
plantation, it is upon the knees of the gods, and not upon the will of
the planter that the variation depends. We cannot, therefore, speak
with accuracy of the separate marginal costs of raw cotton and
cotton-seed. It is true that some plantations are so far distant from
any seed-crushing mill that it is not worth while to sell the seed as
a commercial product; and it might seem, therefore, as though we might
regard the entire costs of cotton growing on _such_ plantations as
constituting the marginal costs of raw cotton. But planters, so
situated, derive a considerable value from their cotton-seed by using
it as fodder for their live stock or as a manure. You can, of course,
argue that proper allowance is automatically made for this factor, as
a deduction from the costs of raw cotton, when you add up the expenses
of the plantation. In the same way you can deduct the price which a
planter who sells his cotton-seed obtains for it, from the total costs